Mitochondrial DNA mutation in an Italian family with Leber hereditary optic neuropathy

Childhood Leber's hereditary optic neuropathy (ND1/3460) with visual recovery

The authors report the clinical features and the results of genetic and biochemical studies of a child affected by ND1/3460 Leber's hereditary optic neuropathy, who demonstrates a persistent visual recovery after protracted monitoring. A 10-year-old male suffered from a severe right visual impairment that was incidentally detected. Within 2 months the left eye was also seriously involved, and visual acuity worsened to 20/300 in both eyes, associated with bilateral cecocentral scotomas and dyschromatopsia. During the following months a progressive visual improvement occurred, and 2 years later the visual acuity was 20/20 OU. After 9 years of follow-up the clinical status is unchanged. The mutation at np ND1/3460 was found to be virtually homoplasmic in the proband's mtDNA, which was extracted either from platelets or leukocytes, whereas the mother and the sister tested heteroplasmic for the same mutation. The specific activity of complex I in platelets was reduced in the proband and normal in his relatives. An abnormal resistance of NADH:ubiquinone reductase to the inhibitory effect of rotenone was found in platelet mitochondria from the proband and family members and was consistent with the degree of heteroplasmy. This pattern of biochemical abnormalities suggests a cumulative effect of the increasing percentage of mutated mtDNA on complex I function, which involves the interaction between complex I and its substrate ubiquinone in the heteroplasmic condition (asymptomatic state), and the catalytic function of complex I, as mutated mDNA turns toward the homoplasmic condition (symptomatic state).

LHON mutations in Italian patients affected by multiple sclerosis

The occurrence of a multiple sclerosis (MS)-like phenotype in subjects carrying mitochondrial DNA (mtDNA) mutations associated with Leber hereditary optic neuropathy (LHON) has suggested that mitochondrial genes may contribute to susceptibility to MS. With the present study 74 unrelated Italian patients (53 females and 21 males; mean age 37.9, SD 9.9, range 20-59) affected by MS with early and prominent optic nerve involvement and 99 normal control subjects were analysed for the presence of primary (nps 11778, 3460, 14484) and an alleged secondary one (np 15257) LHON mutations. A single MS patient carrying a virtually homoplasmic LHON mutation at np 11778 was found. Family history revealed a maternal uncle affected by MS, decreased at age of 64 in consequence of a stroke. The patient's mother harboured the same mutation in a homoplasmic way. Primary LHON mutations were not detected in any other MS patient or control. Of the MS patients 5.4% (4 out of 74), and 5.1% (5 out of 99) of the controls carried the 15257 mutation in a homoplasmic state. Present data do not support any contribution of primary LHON mutations to genetically determined susceptibility in MS. There is no evidence that the 15257 mutation has any pathogenetic significance in the Italian population.

Screening for the two most frequent mutations in Leber's hereditary optic neuropathy by duplex PCR based on allele-specific amplification

This report describes a rapid and inexpensive assay, which allows detection, in whole blood and by PCR alone, of the two most frequent mitochondrial DNA mutations causing Leber's hereditary optic neuropathy. The assay is based on allele-specific amplification, using primers with the mutation-specific base in the 3' position, and a deliberately introduced G-->C substitution of base no. four from the 3' end, which prevents amplification of the wild-type allele.

The NADH:ubiquinone oxidoreductase (complex I) of respiratory chains

The inner membranes of mitochondria contain three multi-subunit enzyme complexes that act successively to transfer electrons from NADH to oxygen, which is reduced to water (Fig. I). The first enzyme in the electron transfer chain, NADH:ubiquinone oxidoreductase (or complex I), is the subject of this review. It removes electrons from NADH and passes them via a series of enzyme-bound redox centres (FMN and Fe-S clusters) to the electron acceptor ubiquinone. For each pair of electrons transferred from NADH to ubiquinone it is usually considered that four protons are removed from the matrix (see section 4.1 for further discussion of this point).